Evidence that central 5‐HT1A‐receptors play a role in the von Bezold‐Jarisch reflex in the rat

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Abstract
1 The effects of intracisternal (i.c.) application of putative 5-hydroxytryptamine (5-HT)1A antagonists on the reflex bradycardia evoked by injection of phenylbiguanide (i.v.) were investigated in anaesthetized, atenolol-pretreated rats. 2 Intracisternal application of spiperone (100 μg kg−1) reversibly attenuated the reflex bradycardia whilst the same dose given i.v. had no effect. The bradycardia was also attenuated by i.e. methiothepin (200 μg kg−1), (±)-pindolol (100 μg kg−1) and buspirone (200 μ kg−1) but was not attenuated by antagonists selective for α1-adrenoceptors (alfuzosin; 100 μg kg−1), 5-HT2-receptors (BW 501C67; 100 μg kg−1) or dopamine D2-receptors ((−)−sulpiride; 100 μg kg−1) given i.e. 3 It is concluded that the 5-HT1A-receptor antagonist action of intracisternally applied spiperone, methiothepin, (±)-pindolol and buspirone is responsible for the ability of these drugs to attenuate reversibly the excitation of cardiac vagal motoneurones caused by activation of the von Bezold-Jarisch reflex.